I think the iPad Pro audio options will be the same as any other modern iPad, you'll just need a USB-C cable and a class-compliant USB interface. Some discussion can be found here: Record SPDIF to iOS

I'm sorry I keep bringing this up but the Scarlett range of interfaces from Focusrite have an issue: if the SPDIF sync source is set to external (needed for SPDIF connection to Kemper toaster & rack I think) then they will not route any analogue audio if that SPDIF master (e.g. Kemper) is not connected and switched on. Maybe they've fixed this now in gen3 models, I don't know. But given you have to find a PC or Mac to change the SPDIF sync source for the interface, it's a pain if your focus is iOS. I'm personally happy to use the analogue connections to my Kemper to get around this, I don't really notice the difference.

Apple's Garageband is free on iPad; if you want to use your interface as a mixer, I recommend AUM from Kymatica for a study on efficient app design! They also do a sound management app called Audioshare that works nicely with AUM. For more heavy duty recording, there are a few DAWs other than GB on iOS, the better known ones being Auria Pro and Cubasis. You will probably find more useful information about these and more on the Audiobus website, though its quite an electronic-music-centred forum... These DAWs all cost up-front (no free demos) so you'll have to research first.

Hope that helps!

Edit: Sorry, I've never tried using an external sound source with video <shrug>